This report describes work performed to evaluate the use of the Global Positioning System (GPS) for low-cost civil air navigation. The report describes a GPS Test and Evaluation (T&E) System developed jointly by M.I.T Lincoln Lab., Standford Telecommunications, Inc., and Intermetrics, Inc., using techniques that could lead to low-cost commercial avionics. System performance results obtained in the laboratory and during flight tests are provided which demonstrate compliance with current and future navigation accuracy requirements for enroute, terminal and non-precision approach flight paths. The report also includes functional specifications for a low-cost GPS navigation system for civil aircraft. The GPS T&E system design was based on the two important features: (1) automatic tracking of all visible satellites (rather than a minimum set of four); and (2) a dual-channel GPS C/A code receiver. Tracking all visible satellites allows the system to maintain continuous navigation when a satellite sets or is momentarily masked during aircraft maneuvers. The dual-channel receiver dedicates one channel to pseudo-range measurements, and the other channel to acquiring new satellites as they become visible. These two features, validated by flight test, allow the system to provide continuous navigation updates during critical aircraft maneuvers, such as non-precision approaches, and during satellite constellation changes. Originator-supplied keywords include: NAVSTAR GPS, air navigation, C/A code receiver, and dual-channel receiver.